1. Field of the Invention
The invention relates to a sensing device, and more particularly to a sensing device with differential capacitance/resistance measurement.
2. Description of the Related Art
A conventional sensing device comprises a sensing array and a detection unit. The sensing array is composed of horizontal sensing electrodes and vertical sensing electrodes, wherein the horizontal sensing electrodes interlace with the vertical sensing electrodes. When an object, such a finger or a stylus, approaches the sensing array, the detection unit can measure capacitances/resistances related to the sensing electrodes to detect the presence of the object and further to determine touch coordinates or a touch position of the object. The capacitances/resistances measured by the detection unit may be mutual-capacitances formed around crossover points of pairs of interlaced horizontal and vertical sensing electrodes, self-capacitances formed between horizontal/vertical sensing electrodes and the object, or resistances formed between horizontal/vertical sensing electrodes and a counter electrode. During the operation of the sensing device, the coupling of noise onto the horizontal and vertical sensing electrodes from surrounding environment may cause errors. Thus, a differential measurement for the capacitances/resistances related to the sensing electrodes is provided to eliminate noise from the surrounding environment.
For the conventional differential measurement, a detection unit comprises only one differential amplifier, and the differential amplifier is coupled to a pair of sensing electrodes to individually generate output signals representing capacitances (mutual-capacitance or self-capacitance)/resistances. In order to measure all of the capacitances/resistances generated in the sensing array, the differential amplifier continuously switches to be coupled to a different pair of sensing electrodes. Thus, for a sensing device with a large sensing array, a detection unit comprising only one differential amplifier takes a long time to measure all capacitances/resistance generated in a sensing array of the sensing device for detecting the presence of an object.